Processing facilities, such as manufacturing plants, chemical plants, crude oil refineries, ore processing plants and the like, are often managed using process control systems. Among other operations, process control systems typically manage the use of motors, valves, and other industrial equipment in the processing facilities.
In conventional process control systems, controllers are often used to control one or more processes that are occurring or being implemented. The controllers may, for example, monitor the operation of the industrial equipment, provide control signals to the industrial equipment, and generate alarms when malfunctions are detected. Conventional process control systems are often responsible for monitoring and controlling numerous process variables, which generally represent characteristics of the process being monitored and controlled.
Fluid stream characteristics are one type of process variable that is frequently monitored in typical process control systems. For example, flow rate, temperature, pH, turbidity, and particulate matter content of a fluid stream may be monitored by sensors of a process control system. Wireless data transmission capability may be desirable for these sensors because fluid stream pipes are often in remote or inaccessible locations or because the necessary wiring would be relatively expensive, would need to be routed through one or several bulkheads, or would add too much weight to a vehicle in which the sensor is located.
However, one difficulty associated with implementing wireless sensors for monitoring properties of fluid streams is the power source needed for powering the wireless sensors. One solution to this difficulty is to use a battery for the power supply. However, this solution is non-ideal because batteries are limited in power supply capability and are not a reliable power source at very low or very high temperatures. Another solution to the power supply problem is to harvest energy from environmental sources, such as air flow, thermal gradient and vibration. One particular method uses a vibrating magnet in a coil, which produces electrical power by the Faraday effect. Another method uses piezoelectric materials attached to a vibrating beam. However, a disadvantage associated with this technique is that power is provided only when the vibration force is applied in a direction that excites the beam.